1. Field of the Invention
The present invention relates to a substrate processing method of and a substrate processing apparatus for processing substrates, such as semiconductor wafers, by, for example, a cleaning process.
2. Description of the Related Art
When processing a semiconductor wafer by, for example, a photolithographic process, a resist film is formed on a surface of the wafer, the surface of the wafer coated with the resist film is exposed to light in a desired pattern, and the wafer is subjected to a developing process to develop the image of the pattern, and then unnecessary portions of the resist film are removed.
A cleaning apparatus is employed for removing the unnecessary portions of the resist film. The cleaning apparatus immerses the wafer in a cleaning tank containing a chemical liquid called SPM (an H2SO4/H2O2 mixed liquid) to remove the portions of the resist film. In view of the protection of the environment, it is desired to remove the resist film by using ozonic water capable of being easily disposed of by a liquid disposal process instead of a chemical liquid. When ozonic water is used,the wafer is immersed in a cleaning tank containing ozonic water and the resist forming the resist film is decomposed into carbon dioxide, water, etc. by an oxidizing interaction between oxygen radicals contained in the ozonic water and the resist film.
Normally, ozonic water is prepared by dissolving a high-concentration ozone gas in pure water by bubbling. The ozone of the ozonic water contained in the cleaning tank escapes from the ozonic water and the ozone concentration of the ozonic water decreases gradually with time. Since the cleaning ability of the ozonic water is dependent on its ozone concentration, the cleaning ability of the ozonic water decreases as the ozone concentration decreases and the ozonic water having an insufficient ozone concentration is often unable to remove the resist film satisfactorily. Since the rate of interaction between ozone and the resist film is very high, only insufficient ozone can be supplied to the surface of the resist film if the wafer is merely immersed in the ozonic water and hence the interaction between the ozone and the resist film cannot be carried out at a high rate. The interaction between ozone and the resist film must be carried out at a high temperature. Therefore, in some cases, high-temperature ozonic water is prepared by dissolving ozone in pure water of, for example, 80xc2x0 C. by bubbling. However, since the solubility of a gas in pure water at high temperature is low, ozonic water of high ozone concentration cannot be produced and hence the interaction between ozone and the resist film at a high reaction rate cannot be achieved.
Accordingly, it is an object of the present invention to provide a substrate processing method and a substrate processing apparatus capable of exercising a high processing ability in processing substrates.
To achieve the object, the present invention provides a substrate processing method comprising the steps of: placing a substrate in a processing vessel; forming a film of a solvent over a surface of the substrate; and dissolving a process gas in the film of the solvent.
To achieve the object, the present invention further provides a substrate processing method including the steps of: placing a substrate in a processing vessel; supplying a vapor of a solvent into the processing vessel; supplying a process gas into the processing vessel; producing a reactive substance by interaction between the vapor of the solvent and the process gas; and processing the substrate with the reactive substance.
The step of processing the wafers with the reactive substance may include a step of forming a film of the solvent over the surfaces of the substrates and a step of dissolving the process gas in the liquid film.
The step of producing the reactive substance by interaction between the vapor of the solvent and the process gas may be a step of forming a molecular layer of a mixture of molecules of the solvent and those of the process gas.
The reactive substance contains atoms, molecules and radicals, the reactive substance produced in a processing chamber is used immediately for processing the substrate before the reactive substance disappears and hence the reactive substance is able to exercise a high processing ability. When this substrate processing method using the reactive substance is used for, for example, removing resist films formed on substrates, the resist films can be properly converted into water-soluble films by hydroxyl radicals produced by interaction between steam, i.e., a solvent, and ozone gas, i.e., a process gas. The process gas may be any suitable gas other than ozone gas, such as chlorine gas, fluorine gas, hydrogen gas, chlorine gas containing reactive radicals, fluorine gas containing radicals and hydrogen gas containing radicals.
To achieve the object, the present invention also provides a substrate processing apparatus including a processing vessel defining a processing chamber in which substrates are processed, a process gas supply section for supplying a process gas into the processing chamber in the processing vessel, a solvent vapor supply section for supplying a vapor of a solvent into the processing chamber of the processing vessel, and a substrate holding member for holding substrates in the processing chamber in the processing vessel.
Desirably, the substrate processing apparatus further includes a substrate temperature adjusting system for adjusting the temperature of the substrates held by the substrate holding member in the processing space in the processing vessel. The substrate temperature adjusting system may be a heater incorporated into the processing vessel or a temperature adjusting gas supply system for supplying a gas of a regulated temperature into the processing space in the processing vessel.